The production of inflammatory cytokines is under both transcriptional and post-transcriptional control. The transcriptional regulation of cytokine gene expression has been thoroughly investigated. However, the regulation at post-transcriptional level remains largely unknown. MCPIP1 is a recently discovered CCCH- zinc finger containing protein, which was originally found to be significantly induced by monocyte chemotactic protein 1 (MCP-1) and thus designated as MCP-induced protein 1 (MCPIP1). The results from us and other groups suggest that MCPIP1 is essential to control inflammatory response and immune homeostasis by controlling cytokine production in immune cells. However, the precise mechanisms by which MCPIP1 governs cytokine production remain unknown. MicroRNAs (miRNAs) have recently emerged as important regulators of inflammatory gene expression. For example, the miRNA let-7 has been shown to directly target interleukin-6 (IL-6) 3'-untranslated region (3'UTR) by pairing with let-7 binding element and silence IL-6 mRNA. Interestingly, MCPIP1 also targets a distinct element of IL-6 3'UTR and promotes IL-6 mRNA decay. Our preliminary studies showed that MCPIP1 was associated with the major components of miRNA-induced silencing complex including GW182 and Argonaut 2 and co-localized with them in GW/P- bodies. Furthermore, MCPIP1 repressed the reporter bearing IL-6 3'UTR in a miRNA-dependent manner. On the other hand, let-7-mediated silencing of IL-6 mRNA is also dependent on MCPIP1. These intriguing results suggest that MCPIP1 is likely to cooperate with let-7 to control IL-6 production post-transcriptionally. As reported that both MCPIP1 and miR-10a can silence IL-12p40 mRNA by targeting its 3'UTR, similar mechanism may also work for the regulation of IL-12p40 production. Our goal in this proposal is to explore the mechanisms of how MCPIP1 interacts with miRNA effector machinery and cooperatively silence cytokine mRNAs and identify the new mRNA targets of this regulatory pathway. To achieve this goal, we will conduct a series of experiments at molecular, cellular and animal levels. Specially, we will: 1) elucidate how MCPIP1 cooperates with miRNAs to silence IL-6/IL12p40 mRNAs; 2) determine that such mechanisms are operative in the setting of septic shock in mice and humans, and contribute to the extent of septic shock in mice; 3) identify novel mRNA targets of MCPIP1 in macrophages. Completion of the proposed project will be expected not only to define a novel mechanism that controls cytokine production, but also likely to suggest novel therapeutic interventions aiming at decreasing the inflammatory cytokine production and preventing/treating human inflammatory diseases.